In recent years, a rechargeable lithium ion battery is increasingly used as a power supply for driving motors of electric vehicles and hybrid vehicles or a power supply for portable devices.
In particular, when it is applied to an electrically powered vehicle, e.g. an electric vehicle and a hybrid vehicle, it is used in the form of a plurality of packed cells (or a battery pack) in order to ensure required output voltage and a required amount of accumulated electric power, which invites a relatively high battery price. Accordingly, reusing/recycling the battery is an important issue in terms of cost, and diagnosing the battery's degradation to determine whether the battery is reusable/recyclable is an important technique.
For example, Japanese Patent Laying-Open No. 2003-7348 (PTL 1) describes a battery provision system and method characterized by determining whether a used battery is degraded. PTL 1 describes a system in which whether a rechargeable battery is degraded is determined and in accordance therewith if the battery is continuously usable it is recharged and resold by a distributor, otherwise it is sent from the distributor to its manufacturer and thus recycled.
Furthermore, Japanese Patent Laying-Open No. 09-232008 (PTL 2) describes a method of recycling a nonaqueous electrolyte used for various types of batteries including a lithium secondary battery. PTL 2 describes a method in which activated carbon is added to a nonaqueous electrolyte and they are agitated together and then left for a required period of time and thereafter an added liquid is filtered to remove the activated carbon for recovery. This can remove a substance that is a cause of degradation in the added liquid that is adsorbed by the activated carbon to recover the electrolyte from degradation.
As a technique of diagnosing degradation of a rechargeable battery, Japanese Patent Laying-Open No. 2008-241246 (PTL 3) describes a device based on a battery model expression to estimate a state on-line to estimate a state of a rechargeable battery. The document describes that the state estimation device has a characteristics map previously prepared of how a parameter in the battery model expression varies in value from that before use as the battery's state varies, and while the rechargeable battery is in use the device determines a parameter based on the battery model expression and obtains a ratio of the value of the determined parameter to that of the parameter before use corresponding to the battery's current state, (i.e., a rate of change) and diagnoses degradation of the battery.
For a rechargeable lithium ion battery, Japanese Patent Laying-Open No. 2009-63555 (PTL 4) describes whether a rechargeable lithium ion battery mounted in an externally rechargeable vehicle has lithium deposited therein is determined based on reduction of externally electrically charged full charge capacity. PTL 4 further describes that if it is determined that there is deposition of lithium, then, electrically charging/discharging the rechargeable lithium ion battery is restricted in using the battery. Furthermore, Japanese Patent Laying-Open No. 2009-199936 (PTL 5) describes that how many times a lithium secondary battery is electrically charged, how long it is operated, and other similar usage history information are referred to to calculate an amount of lithium deposited in the battery on the negative electrode. PTL 5 further describes starting controlling based on an amount of lithium deposited, as calculated, to dissolve and thus remove dendrite.